Radiotherapy apparatus, also referred to as LINACs (linear accelerators), principally serve to administer a radiation dosage to a patient at a predetermined point on the body to treat a tumor. In such applications, it typically is desirable to take further transillumination recordings of the patient's body shortly before or during the treatment, either to check the positioning of the body or to determine any changes in treatment target area. In order to realize this, x-ray imaging is commonly employed, and in this regard DE 100 51 370 A1, for example, shows a radiotherapy and/or radiosurgery array that includes two x-ray sources. The x-ray sources are arranged above a patient couch and radiate downwards onto an image detector on the patient couch. By comparing the two-dimensional x-ray images obtained with virtual, digitally reconstructed x-ray images from previously acquired CT (computer tomograph) recordings, patient shift from a current position with respect to a desired position can be determined and the patient can be re-positioned accordingly.
Using such two-dimensional x-ray images alone allows deviations in the patient's position with regard to the translational and rotational degrees of freedom to be determined and corrected. If in addition, however, deformations within the irradiation region are to be determined on an ongoing basis, a volume data set must be produced. As a possible solution in this respect, WO 01/60236 proposes a system that includes a linear accelerator and an x-ray assembly in which the x-ray source and the image recorder are arranged transversely on a gantry and horizontal with respect to the LINAC radiation path. In this regard, the x-ray assembly and the LINAC gantry form a unit.
It is disadvantageous in principle to attach additional apparatus and therefore more weight to the LINAC gantry. The LINAC gantry rotates in a predetermined way and into predetermined positions, and additional weight impedes this rotation and makes it more difficult to maintain particular pre-sets in the rotating procedure, and therefore reduces the precision of the irradiation process. Another disadvantage of such systems is that they are only provided as a whole (i.e., as a complete unit), such that upgrading or retro-fitting other systems is not possible or extremely difficult.